Spent yesterday in a small under stairs store sorting out a consumer unit; the 100 Watt lamp soon felt very hot close to my head. Done some research and found the following amazing facts: 1˚C = 0.52752793 Wh [Watt hour]. The 100W incandescent lamp produces 2.1% light and 97.9% heat. So the actual heat output was 185.6 ˚C. That’s pretty hot, 2 feet from my head!